Effect of Precursor Composition on Ion Migration in Hybrid Perovskite CH₃NH₃PbI₃

We used thin-film transistors (TFTs) to understand the effect of precursor composition on ion migration in the hybrid perovskite CH₃NH₃PbI₃(MAPbI₃). For all the precursor compositions we investigated (i.e. MAI/PbI₂ ratios of 0.5, 0.8, 1.0, and 1.2), the TFTs exhibited anomalous hysteresis in their current-voltage (I-V) characteristics, indicating mixed ionic-electronic conduction. The hysteresis in the TFTs with MAI/PbI₂ = 0.5 was the largest, followed by that of the TFTs with ratios of 1.2, 1.0, and 0.8. Although residual PbI₂ was the source of hysteresis in the PbI₂-rich TFTs (MAI/PbI₂ = 0.5), we conclude that it may enhance electronic conduction and minimize ion migration when present in small amounts (as in the case of MAI/PbI₂ = 0.8).